Introduction to String Theory
String Theory is basically a theory that postulates that all particles are really extended objects. In the old, canonical String Theoryies, these extended objects are Strings. The vibrational modes of these strings determine the properties of the emergent particle. The rotational modes of these strings determine the Spin in the RNS Formalism. Importance Currently, String Theory is studied because it is a suitable candidate for a Theory of Everything. In other words, it can describe all interactions, and matter, using a simple gauge group or a square of a simple gauge group. It also allows for a Quantised version of General Relativity, and thus a theory of Quantum Gravity. Of course, every Theory of Everything is by definition also a theory of Quantum Gravity (but not vice versa). History Historical Motivation 1961 to 1968 The Historical Motivation behind String Theory was that it would probably describe hadrons. However, it was found to be an incorrect theory, as it predicted only bosons, and predicted a Tachyon. This early version of String Theory is called Bosonic String Theory. Quantum Chromodynamics, instead, became the "correct" theory of hadrons. String Theory was for the most part, discarded by many physicists. Strings 1969 When String Theory was initially discovered, it was S-Matrix Theory. It was all about S-Matrices, Regge Trajectories, and all that; but there was no concept of Strings involved. With the discovery of the Nambu-Goto Action by Yoichiro Nambu and Tetsou Goto, it became clear that String Theory was a theory of Strings. This was actually a follow-up to the discovery of Strings by Leonard Susskind, Holger Biech Nielson, and Yoichiro Nambu. This action was later expanded/modified into the Polyakov Action by Brink, Di Vecchia, Howe, and Tucker. This became known as the Polyakov Action when Alexander Polyakov included it in one of his textbooks. Supersymmetric Revolution (1970-1981) Pierre Ramond discovered Supersymmetry, to be specific, Worldsheet Supersymmetry. He discovered that adding spacetime vectors as "fermionic fields" allows the arisal of fermions in String Theory. This can be seen from the RNS Action, with certain elegant Supersymmetryic transformation invariance. However, Pierre Ramond worked only with periodic boundary conditions for the fermionic fields. Meanwhile, inspired by this work, Andre Neveu, and John Schwarz worked with anti-periodic boundary conditions. All this eventually lead to the discovery of the RNS Formalasim; when it was eventually realised that the work by Pierre Ramond was compatible with the work by Andre Neveu and John Schwarz. This was followed by the discovery of the GS Formalism by Michael Green and John Schwarz. This formalism had explicit Spacetime Supersymmetry. The RNS Formalism, however, had the problem of a Tachyon in it's ground state, signifying an unsthable Spacetime. This problem was absent in the GS Formalism, however. First Superstring Revolution The First Superstring Revolution was a period during which various discoveries were made, including the GSO Projection, and the discovery of the 5 consistent Superstring Theoryies. Michael Green, Joel Scherk, and David Olive discovered the GSO Projection which maps out the Tachyon from the RNS Formalism. In the same paper, they found that there are 2 ways to apply the GSO Projection; one that preserves Chirality, and one that doesn't. Second Superstring Revolution The Phenomenological Era Experimental Tests Of Supersymmetry Of String Theory itself Applications In Condensed Matter Physics In Fluid Dynamics In Quantum Field Theory Category:Under Construction